Here are some useful and free tools for Web Application troubleshooting: 

  1. IE Developer toolbar (allows editing of loaded pages)  http://www.microsoft.com/downloads/details.aspx?FamilyID=e59c3964-672d-4511-bb3e-2d5e1db91038&displaylang=en 
  2. Fiddler (inspection of HTTP and HTTPS request traffic) http://www.fiddler2.com/fiddler2/  
  3. Firebug add on for FireFox (allows monitoring of page load times, file sizes, etc). http://www.getfirebug.com/ 

John